Enclosed rotor full water flow waterjet propulsors have been commercially available as marine propulsors for many years. Compared to conventional propellers they offer the advantages of shallow draft, a reversing system that does not require a gearbox, reduced underwater noise, more even engine loading, and the safety and damage resistance of enclosed rotors. However, even with the aforementioned advantages they have not been overly successful in market penetration compared to propellers.
They are generally not as efficient as propellers even when their reduced appendage drag compared to propellers is considered. This is especially so in smaller sizes and/or at low vehicle speeds. They also suffer from a more narrow design speed range of efficient operation with part of that limitation due to a restriction for operation at low boat speeds and high power levels where rotor vane cavitaion can occur. They are also generally several times as expensive as a comparable power propeller drive system.
The instant invention offers greater efficiencies than the standard water jet and also provides a way to vary rotor flow and power absorption thereby insuring greater off design efficiencies. Further, due to its unique concept rotor that operates only partially submerged during normal operation, it is mostly immune to cavitation damage.
Normally, during vehicle high speed operation, the preferred embodiment of the instant invention uses only the lower part of the rotor to pump water while the upper part pumps gases that are ambient air (gas) and/or engine exhaust gas. The gas is normally injected upstream of the rotor. Because of its operating parameters, applicant has coined the name Hydro-Air Drive, and its acronym HAD, for the propulsor presented herein as the instant invention. The immediately following discussion is made to show a reason for higher efficiencies of the instant invention.
Measurements have been made by Pratt & Whitney Aircraft and others of the efficiency of inlet pressure recovery in standard water jets. These have shown that inlet pressure recoveries, measured just upstream of the rotor inlet, average above 90 percent over the bottom half of the rotor and closer to 55 percent over the top half. This results in overall inlet efficiencies of only about 70 percent. It is obvious that, since the instant invention's rotor sees the majority of its inlet water flow over its bottom half, the instant invention realizes inlet efficiencies of at least 90 percent. When this is factored into the thrust calculations, the instant invention shows improved thrust values vis-a-vis the standard full water flow rotor water jet. This improvement increases with vehicle speed as the inlet pressure recovery is a bigger part of overall pressure head available at the rotor discharge at higher vehicle speeds. For example, the calculated thrust for the instant invention is approximately twenty percent higher at a vehicle speed of 40 knots. By way of definition, vehicle speeds of up to fifteen knots are considered as low speed and vehicle speeds over fifteen knots as high speed for purposes of this application.
Haglund, International Patent Publication Number: WO 88/05008, has a means to inject air into a water jet housing. Haglund proposes a means to plug the discharge of a water jet nozzle when the jet is not in use by means of an inflatable ball plug. He then pumps air into the waterjet to displace all of the water in the pump housings. The benefit of this is to keep the pump housing and rotor clear of growth and contamination when not in use for extended periods. It would be possible to inject air into the water upstream of the rotor in Haglund's water jet when the rotor is rotating and pumping water. However, there is no way to separate the air from the water by a waterline with the rotor rotating and pumping so a turbulent mixture of air and water would result. This actually serves to decrease the efficiency of Haglund's water jet since the turbulent mixture of air and water decreases the efficiency of his rotor. This is actually the case and the intent of Joyner et al., United Kingdom Patent GB 2141085A, who has gas injection means upstream of his water jet rotor and states "By providing the means for introducing gas into the water intake casing and for varying the amount of gas introduced (which means can be a simple bleed valve), the efficiency of a unit can be decreased in accordance with the amount of gas introduced is important to state here that the instant invention has means to create a separation of gas and water upstream of the rotor and does not have a turbulent mixing of gas and water upstream of the rotor vanes as is the case with Haglund and Joyner et al. who have no means to separate the gas and water upstream of the rotor.
In a related technical development, water jet rotor air injection tests were run at Pratt & Whitney Aircraft in 1967-69 in attempts to reduce cavitation damage to the rotor of a 3,200 HP water jet. It was felt that the presence of air would absorb some of the material damaging explosive forces on the rotor blades caused by collapsing cavitation vapor bubbles. The air was injected upstream of the rotor in a similar manner to that shown by Haglund and Joyner et al. and did indeed reduce the rotor cavitation damage since the air was automatically thoroughly and turbulently mixed into the incoming water. However, air volumes of only a few percent of total rotor flow volume were possible before a very sharp decrease in rotor efficiency occurred. These tests proved that a simple turbulent mixing of air into the water upstream of a rotating waterjet rotor, which is the only effect that Haglund's and Joyner et al's systems could provide, actually has a detrimental effect on water jet performance. The instant invention has a clear separation of the water and gas upstream of the rotor as is defined by a waterline in the preferred embodiments. The separating waterline is insured by use of a means to direct the water prior to its reaching the rotor in the instant invention.
Smith, U.S. Pat. No. 3,785,327 has an engine cooling water pickup positioned upstream of his rotor which cannot dispense gas into his water inlet. He has a high resistance forward facing or reverse hinged inlet flap for restricting and/or shutting off water flow to his rotor. Partial closing of Smith's inlet flap will only result in a pressure drop in the liquid flow supplied to his rotor. Critically important is the fact that Smith has no means to inject gas into the rotor inlet and therefore cannot have a separation of gas and liquid at the rotor inlet as is a primary requirement of the instant invention. As such, there is no relation between Smith's invention and the instant invention
Further, the instant invention uses a special rotor that operates similar to a surface piercing propeller and does not, in its preferred embodiment, use a full water flow nozzle to control flow and velocity of water downstream of the rotor and out of the water jet which is normal and required for state-of-the-art waterjets. Instead, the instant invention uses a mostly open discharge, sometimes aided by efficiency improving flow straightening vanes, that allows water and air to discharge freely out the back of the drive. The result of all of this is that the instant invention offers a dramatic departure from and dramatic improvements over existing water jet design technology..
There are some propeller systems that operate with only portions of the propeller submerged as exemplified by Van Tassel U.S. Pat. No. 4,941,423 and Kruppa et al. U.S. Pat. No. 4,371,350. These type of propulsors are normally called surface piercing propellers. Both operate with the lower portions of their propellers exposed which differs extensively from the preferred embodiment of the instant invention which has a housing essentially fully around its rotor in an encircling manner. The instant invention's use of an inlet housing and encircling rotor housing and/or rotor vane ring results in greater rotor efficiencies but at the expense of some additional resistance since the lower portion of the housing is exposed to the passing water. The instant invention has overcome most of the just mentioned housing resistance since the majority of its housings are behind the transom and/or inside the boat hull. Because they do not have fully or even partially enclosing rotor housings and therefore have propellers that are exposed over substantially the entire lower half of their rotation, the inventions of Van Tassel and Kruppa et al. bear little resemblance to the instant invention it be noted that the instant invention can be configured with a majority of the upper half of its rotor exposed and free of structure while the majority of the lower half of its rotor is enclosed which is the exact opposite of Van Tassel and Kruppa, et al.
Guezou et al. U.S. Pat. No. 4,929,200 presents a waterjet that has air injected downstream of the rotor in the stator section. The purpose of this, according to the inventor, is to agument thrust with large amounts of air mixed with the water of the rotor. Guezou has a rotor that is supplied with water from a fluid filled duct so there is really no relation of Guezou and the instant invention that uses an approximately half full rotor portion at high vehicle speeds.
The instant invention also offers a new simple steering and reversing system. It consists of independently steerable side rudders and/or a center rudder in the preferred embodiments. When reversing is desired, it is possible to prevent flow from discharging aft by deflecting the steering rudder(s), or by other water flow blocking means, such that they block the discharge passageway. By so doing, water is then directed to a maneuvering device that can accomplish full 360 degree maneuvering in its preferred embodiment. The maneuvering device(s) include a nozzle that is normally oriented in a forward position when it is not use to offer a minimum or resistance to water discharging from the rotor vanes. It is also preferably shielded by a deflector step to prevent water that is going astern from hitting it.
In the preferred embodiment of the instant invention, the steering rudders are driven through right angle gears by servo motors located inside the hull. Other means of driving the rudders are within the scope of the invention, however, the servo motors are preferred as they are simple and reliable.
Side rudders are shown by Hamilton U.S. Pat. No. 3,007,305 and 3,233,573 however, his side rudders operate in unison and are positioned aft of a vertically operating reversing gate. Hamilton accomplishes steering in reverse by means of steering the rudders. As such, there is little resemblance to the simple compact design of the instant invention with its rotatable angled maneuvering device(s). An added feature of the instant invention is that maneuvering, normally a full 360 degrees, is possible while the water flow is blocked from discharging to the rear.
Macardy et al. U.S. Pat. No. 3,824,946 and Van Veldhuizen U.S. Pat. No. 4,421,489 present, respectively, a water jet steering system and an air propeller propulsor both with side steering rudders. They have means to control the side rudders or steering blades such that they can go perpendicular to the discharge flow. This has the effect of blocking the discharge flow and forcing it to reverse and/or go sideways to accomplish reversing. Neither Macardy nor Van Veldhuizen has a rotatable maneuvering device(s) as does the preferred embodiment of the instant invention. As such, neither can supply 360 degree rotatable maneuvering forces with the flow blocked from discharging aft as can the instant invention. Because of the foregoing reasons, there is obviously little resemblance between Macardy's and applicant's instant invention.
Joyner et al., United Kingdom Patent GB 2141085A, offers a marine pump with a 360 degree steerable discharge that is only useful as a low speed maneuvering system. This is because the pump discharge flow is always discharged downward and to the discharge maneuvering system which results in high internal flow losses and high underwater drag. The instant invention offers the maneuvering capability of Joyner et al. when its discharge flow is blocked from going straight rearward; however, the instant invention has a free opening directly behind the rotor vanes that discharges rearwardly directly in-line with the rotor shaft centerline when the instant invention is in the high speed forward mode. There is no flow through Applicant's maneuvering device unless there is a blockage of flow rearward from the rotor vanes while Joyner et al. always has rotor discharge through his maneuvering system as he has no other way to discharge fluid from his rotor vanes. There is also no excessive underwater drag with the instant invention as its maneuvering device components are, at least primarily, free of water flow from under the boat. As such, there is little resemblance between Applicant's instant invention and Joyner et al.
Mamedow, German Patent 2,217, 171, has a reversing system that includes a series of louvres inside of a steering ring to accomplish 360 degree steering when flow is blocked from exiting rearward by a steering flap. Mamedow's louvres are set in a full circle and as such are subject to direct impingement by water discharging from his rotor and from water exiting below the boat when in the normal full speed ahead mode of operation. Applicant's invention's use of discharge nozzle(s) or orifice(s) biased to one side of his maneuvering device acts to prevent water from hitting the nozzle openings when in the normal ahead mode of operation. Applicant's invention normally would have his maneuvering device set into a forward thrust orientation when not used for maneuvering. Further, applicant offers a step to break the water flow from hitting the nozzle openings in his maneuvering device during normal full speed ahead operation. Also, the instant invention offers multiple maneuvering devices, each having nozzles, that have coordinated movement to reduce overall axial length requirements. These notable improvements in concept clearly define over Mamedow's patent.
Applicant's instant invention offers other features. Importantly included is an optional rotatable curved, preferably circular arc shaped, inlet water directing valve that, when in the low boat speed closed mode, directs water to the full 360 degrees of rotor rotation. This is accomplished by means of the Coanda Effect whereby water flow tends to follow curved surfaces. Other inlet valve and/or structural discontinuities are also offered as ways to separate water and gas flows from upstream of the rotor. Another very important feature is that the inlet valve can act as a means to control gas flow, including a complete shut off of gas flow, to the rotor vanes.
Other features of the instant invention include an attractive cover that shows no cables, gears, or other such moving parts, a simple bearing oil fill and check plug located inside the boat, a means to discharge the engine exhaust simply and cleanly into the rotor which also improves engine performance since the rotor is drawing or aspirating the gas discharge from the engine, an inset in the housing for a rotor vane ring with such inset being supplied with gas to reduce water drag on the rotor vane ring, a blade like attachment to the inspection cover that slices weeds, rope, etc. between the blade like attachment and the front end of the rotor, and a means to vary flow into the rotor and thus effect water discharge velocity, power consumption, and performance.
Further notable advantages are derived from use of the rotor vane ring inset into the housing. First, the overall hydrodynamic efficiency is raised because the rotor vane ring acts to reduce rotor blade tip leakage. There is little penalty for this rotor vane ring since its periphery sees mostly air rather than water in its preferred embodiment and therefore has little drag. Also, since the rotor vane ring is inset into the housing it has little hydrodynamic resistance in the main flow path. Second, and very importantly, the rotor vane ring makes for a structurally sound rotor so less expensive rotor materials can be used. Third, since, due to the rotor vane ring, there is little or no abrasive action between sand or other particles and the housing in the area of the rotor vane ring it is possible to use less expensive housing materials. For example, most water jet designs use stainless steel housings around the rotor while the instant invention, when equipped with a full shroud type rotor vane over the full longitudinal length of the rotor blades, can use structural foam, fiberglass, or other less expensive materials.